Tallest Tress Unveiled

From Left: The tops of old redwoods have often been killed in crown fires long ago. Eventually they regrow new vibrant crowns, such as this tree is doing here. Middle: Huckleberry bushes grow from pockets of decaying wood and soil high up in tall redwoods—a handy snack for scientists performing canopy research.Right: The first branches on tall redwoods are often 150 feet or more above the ground. For climbers, the view can be intimidating.

STEVE SILLETT FELT EXHILARATED as morning sun rays burst through the redwood canopy. He was dangling from ropes in one of the world’s largest trees as a National Geographic photographer snapped pictures. For eight days straight, Sillett, his team of climbers and photographer Nick Nichols had risen before dawn and climbed this tree, hoping to get the perfect shot of Sillett and his team positioned throughout its crown. Nichols had already taken thousands of pictures. Finally, Sillett thought, they had nailed it.

“We looked at the images and they were awesome,” Sillett recalls. “But Nick says, ‘I think we can do better.’ So for six more days we went out. The guy is relentless.”

Top: Sillett near the top of a 371-foot-tall redwood inspecting sensors that measure air humidity, temperature and leaf wetness.Bottom: Sillett inspects equipment 250 feet above the ground around a large fern mat. Large redwood crowns often harbor heavy loads of leather-leaf fern; its decomposing mass is the main component of arboreal soil, which can reach depths of up to three feet.

The same could be said about Sillett, one of the world’s leading forest scientists and the Kenneth L. Fisher Chair of Redwood Ecology at Humboldt State University. He climbs tall trees about 100 days a year, spending fall and winter in the coast redwoods and summers in the giant sequoias of California’s Sierra Nevada. In between, he travels the world to locate, climb and study tall trees. “My work is my hobby. I don’t consider it work,” he says.

In 2007, Sillett was featured in Richard Preston’s book The Wild Trees. It chronicled the hunt by Sillett and colleagues for the world’s tallest redwood, which Sillett climbed to confirm its height: 379.1 feet—70 feet taller than the Statue of Liberty. The discovery and book made Sillett a legend among tall-tree climbers and provided the public with its first glimpse into the crowns of ancient redwoods, where few had previously dared venture.

Sillett and the redwoods are now getting their next close-up. The October issue of National Geographic magazine will feature a cover story about coast redwoods, and an accompanying hourlong documentary will be aired on the National Geographic Channel. Sillett devoted months to the magazine and documentary, which will be seen by millions, and says they are mind-blowing.

“We did a shot where the camera is being lifted by counterweights and panning through the canopy so you get the sense that you’re flying through the forest,” he says. “There are shots where the camera is zooming by while we’re climbing. It’s going to be sweet.”

For Sillett, working with National Geographic was a chance to educate the public about the seldom-seen crowns of tall redwoods, which support a rich community of life including huckleberries, ferns, salamanders and other creatures. “It’s hard to fully appreciate these trees from the ground. You can tell they are awesome, but you don’t know the half of it.”

Sillett hopes the media coverage will inspire the public and spur funding for scientific research on tall trees around the world.

Coast redwoods, which extend from Big Sur to southern Oregon, have survived for more than 10 million years. Until the last ice age they grew widely across the northern hemisphere and in the area that is now Oregon and Washington. Sillett calls them “super heroes.” They resist rot and are nearly impervious to fire. Nothing eats them. They can grow in deep shade. “All these things promote great longevity. Once a redwood is there, it stays, and once a forest is established, it cannot be defeated. Unless it is logged.”

Hired at HSU in 1996 to teach botany, Sillett has since moved to the Department of Forestry and Wildland Resources, a post where he hopes to do nothing less than rewrite the book on how redwood forests are managed. Ninety-six percent of the old-growth redwood forest has been logged. “I’m not anti-logging,” he says during a recent visit to Prairie Creek Redwoods State Park and Redwood National Park, where much of the National Geographic filming took place. “I have no problem cutting trees. I just think we can do a better job of picking the trees we cut.”

Sillett believes forestry could benefit by learning the science of arboriculture. “Arborists know how to promote tree health. I hope to stimulate a marriage between arboriculture and forestry.” Current timber practices produce low-quality lumber by cutting redwoods before they have time to grow dense, rot-resistant heartwood. By selectively thinning timberlands and allowing some trees to mature, the lumber industry could get high-quality wood back into the marketplace and promote healthier forests. “Historically, redwood was the best. It built San Francisco twice. But look at the wood being sold today. There is a little core of hardwood, and the rest is sapwood. It’s junk.”

Top: These are the highest leaves on earth; the crown of this redwood in Redwood National Park sits more than 379 feet above the ground.Left: To quantify data about an entire tree, researchers cut branches and measure them for bark, sapwood and heartwood—the dark red centers.Middle: The scientific equipment in the lab includes these housings for air temperature and humidity sensors.Right: Samples collected in the forest are meticulously stored and documented for research in the lab.

Sillett is a man of strong opinions and intense drive. While others study redwoods from the ground, Sillett goes to the top. He combines the intellect of a leading scientist with the adventurousness of an elite climber, and his studies about redwood physiology are changing conventional wisdom.

For instance, scientists once believed redwoods grew slower as they aged. “Our work is demonstrating that’s not true. These trees,” he says, waving his arms at the giant redwoods surrounding us in Prairie Creek, “are adding more wood than at any point in their lives.” His studies of redwood growth rings, obtained by taking core samples from various heights, are providing the most accurate age estimates ever for living trees. “We are able to take these trees back through time and estimate when they were zero age. That’s never happened before.” Sillett has determined that one of the largest coast redwoods he’s studied is at least 1,850 years old, give or take 100 years.

“Most scientists are incrementalists,” says Ken Fisher, an HSU alumnus and financial advisor whose endowment provides Sillett with a $100,000 annual research budget. “They work in baby steps. They don’t do anything radical. Steve is different. He wants to do transformational research that allows us to make quantum leaps forward. He’s not constrained in his thinking. That’s what attracted me to him.”

This fall, Sillett expects to launch a groundbreaking study into the effects of climate change on redwoods. Funded by the Save the Redwoods League, Sillett and collaborators will establish research plots in all the major parks and reserves for coast redwoods and giant sequoias.

The study team will include a dream team of redwood scientists. Sillett and U.C. Berkeley professor Todd Dawson, who did pioneering research about the utilization of fog by coast redwoods, will be co-directors. Robert Van Pelt of the University of Washington will be the lead scientist. Anthony Ambrose, a Berkeley post-doctoral researcher who studied the effects of height on redwood physiology with Sillett, will analyze carbon and oxygen isotopes in the tree rings to see how redwoods have responded to past climatic changes.

Top: The journey to the top of a 300-foot-tall tree takes an experienced climber about 20 minutes; climbers tend to start their day of data collection near the treetop and then work their way down.

“Working with Steve is challenging and rewarding,” says Ambrose, who earned his master’s degree under Sillett at HSU in 2004. “He has high standards and demands the best performance and the most rigorous science.”

Initial climate data are already yielding fascinating insights. Redwoods in Humboldt Redwoods State Park appear to have undergone a growth spurt during the 20th century. Sillett hypothesizes this may be due to increasing atmospheric carbon dioxide—so-called CO2 fertilization.

Climate change is a concern because redwoods are adapted to specific growing conditions. Coast redwoods, which get water from rain and fog, should endure because the North Coast is expected to change less than other regions (although the trees will probably contract to the south). Giant sequoias, however, are in more trouble. Sequoiadendron giganteum gets water from mountain snow, which is decreasing with climate change. “Giant sequoias are vulnerable,” Sillett says. “I’m worried about them.”

As conservationists and governments promote forest growth to moderate the impacts of climate change, Sillett believes these super-hero trees could help. “Pound for pound, no species soaks up and effectively stores more carbon than redwoods,” he says. “If there is interest in creating large forest reserves whose primary purpose is carbon sequestration, then why wouldn’t you plant the most successful carbon sequesterers the Earth has ever produced? It’s something to consider.”

Back in the park, Sillett stops his car to admire a tall tree where he filmed with National Geographic. His yearlong sabbatical is about to end, and he has a pile of work to complete: journal articles to write, lab results to analyze, preparation for the new course he will be teaching on Silvics/Tree Physiology. He and his wife, HSU lecturer Marie Antoine, a tall-tree climber herself, just finished building a house, which is sided with salvaged redwood. And Sillett recently returned from Australia, where for seven years he has studied the southern hemisphere’s tallest species—Eucalyptus regnans. Catastrophic wildfires swept through southeastern Australia before Sillett’s most recent visit, killing the 300-foot eucalyptus forest. “All of our trees burned. Every one of our study trees is standing deadwood.”

Top: Sillett sets up a robot called a Gigapan, which takes hundreds of photos along a regular grid that can then be digitally stitched together to create a highly detailed composite image.

The news was more joyous in Tasmania, where Sillett climbed and measured a 327-foot eucalyptus, the world’s tallest. He also joined an expedition in New Zealand that located the country’s tallest known tree—a 224-foot redwood planted in 1901.

Sillett helped popularize many of the tree-climbing techniques now used by researchers worldwide. First he shoots an arrow attached to fishing line over the lowest sturdy limb, sometimes over 200 feet up. He ties tactical rope to the fishing line, hauls up the rope and ascends to the limb. Then he tosses weighted ropes over successively higher limbs and climbs until he reaches the crown, where he unhitches from the main line and uses multiple ropes attached to his harness to travel through the canopy, sometimes from tree to tree—a technique called skywalking. Author Richard Preston’s descriptions of Sillett’s daring climbs are some of The Wild Trees’ most riveting passages.

Sillett has mixed emotions about the book. On one hand, Preston helped educate the public about the redwood canopy. “It gave people a window into part of the forest they would never experience.” On the other hand, it instigated a rush by tall-tree fanatics to find the tallest trees, whose whereabouts were closely guarded.

Top: Hardhats, harnesses and climbing rope are part of the standard equipment for climbing redwoods safely.

In hindsight, Sillett thinks it was a mistake to name the tallest trees. He and colleagues no longer do so, instead assigning numbers. “Naming a tree makes it a celebrity. When you give it a mythological name, people say, ‘I’ve got to go see it.’ We don’t want to make these trees targets of visitation.” The crown on the most-visited tall redwood has died in the past several decades, and Sillett thinks there may be a connection.

Sillett’s days of bushwhacking through impenetrable underbrush in search of the tallest trees are over. Have they all been found? “Yes,” Sillett says definitively. New airplane-mounted laser technology called LIDAR has allowed researchers to locate all of the 350-foot-plus redwoods in Redwood National and State Parks as well as Humboldt Redwoods State Park. There are over 170. “We’re done finding the tallest trees.”

Sillett is now embarked on a new quest. “The next frontier of discovery is finding the largest trees by volume.” General Sherman, a giant sequoia, is the largest of all, but for other species the largest individuals may still be undiscovered. That seems likely. After all, until Sillett and his colleagues began looking, the tallest redwood was thought to be 367.8 feet.

Sillett parks at a trailhead and walks to a redwood with a hemlock tree swirled around its trunk like a snake. He shows this curious sight to a park ranger, who has never seen it. We proceed to an immense redwood he has eyed for many years. He places his hands on the trunk, as if touching an old friend, and stares up. “That’s something, isn’t it?” he says of the tree, which he has never climbed. “Maybe it’s time.”

FACULTY AND RESEARCHERS AT WORK ON FOREST ECOLOGY

Redwood forests are complex ecosystems offering many challenges to scientists. In addition to the work of Steve Sillett, numerous Humboldt State professors and researchers are working to expand our understanding of forest ecosystems. They include: